The purinergic 2X7 (P2X7) receptor is a ligand-gated ion channel which is activated by extracellular ATP and is present on a variety of cell types, including microglia in the central nervous system and other cells involved in inflammation and immune system function. The P2X7 receptor has been shown to have a role in cytolysis in the immune system (Surprenant, et al. Science, 272, 735-41, 1996), and is involved in activation of lymphocytes and monocyte/macrophages leading to the increased release of pro-inflammatory cytokines (e.g., TNFα and IL1β) from these cells (Ferrari, et al. Neuropharmacol, 36, 1295-301, 1997).
Studies have shown that inhibiting P2X7 receptor activation in situations of inflammation (e.g., rheumatoid arthritis and other autoimmune diseases, osteoarthritis, asthma, chronic obstructive pulmonary disease and inflammatory bowel disease) or interstitial fibrosis results in a therapeutic effect (DiVirgilio, et al. Drug Dev Res, 45, 207-13, 1998). These and other studies indicate that P2X7 receptor antagonists may find use in the treatment and prophylaxis of pain, including acute, chronic and neuropathic pain (Chessel, et al, Pain, 114, 386-96, 2005).
Inhibiting P2X7 activation may also diminish or reduce cell death caused by prolongation of activated P2X7 receptors, indicating a potential therapeutic intervention for said antagonists in nervous system injury or degeneration (Sperlagh, et al., Progress in Neurobiology, 7, 327-346, 2006). Vianna, et al. (Epilepsia, 43, 27-229, 2002) also revealed a potential role for P2X7 receptors in the pathogenesis of epilepsy. Interestingly, because of the P2X7 receptor's role in microglia activation and proliferation in the central nervous system (CNS), a self-propagating cycle of neuroinflammation and neurodegeneration results from P2X7 receptor activation in areas of the brain (Monif, et al, J Neurosci, 29, 3781-91, 2009).
Thus, P2X7 receptor antagonists, particularly small molecules with sufficient brain-penetrable properties, are desirable as useful agents for therapeutic intervention in the central nervous system for treating pain, inflammation, neurological and neurodegenerative disorders, neuropsychiatric disorders, or other disorders for which the reduction or otherwise stabilization of pro-inflammatory cytokines is beneficial. The present invention fulfills this need, and provides further related advantages.